1. Field of the Invention
The present invention relates to an optical apparatus which can optically detect a direction of a gazing point (direction of a viewing axis) to control the operation of the apparatus, and, more particularly, it relates to an optical apparatus which can compensate for the difference between the direction of the gazing point and a visual axis optically determined, thereby notably improving the operability of the optical apparatus camera or the like.
2. Related Background Art
Recently, the automaticity and/or intelligibility of cameras have been improved due to the remarkable progress and/or decreased cost of photoelectric converting devices such as an electronic circuit and a CCD. For example, auto focus adjusting cameras have been widely used in not only silver chloride cameras but also video cameras, and an auto exposure adjusting function has been incorporated into almost all cameras.
These automatic functions contribute to a remarkable improvement of the operability of the cameras and have the notable merit that anyone can take a photograph at a constant level without a good photo taking technique.
On the other hand, however, in some cases, the picture framing operation is limited due to restrictions on the hardware of such automatic mechanisms resulting from the fact that the automatic functions are incorporated into the camera. The most important problem is that, since both the auto focus adjusting mechanism and auto exposure adjusting mechanism are constructed to act on a central portion of a view field preponderantly, a greater part of framings of the pictures has an object positioned in the center of the picture. Particularly, since, in the focusing operation, an operator must aim at a main object correctly and it is meaningless to consider an average focus of the whole picture, it is indispensable to frame the picture so that the main object is positioned at a position where the auto focus detection device acts on the main object.
In order to avoid such restrictions on the framing of the picture, a method called as "focus lock" has been normally used. According to this method, in a half-push condition of a shutter button of a camera, when an operator has set or positioned the main object in a central position of the field, the auto focus adjusting mechanism provided in the camera operates to focus the main object. When the main object is focused, the auto focus adjusting mechanism is automatically locked. Then, the operator shifts the main object in a desired position in the field to obtain a desired framing, while maintaining the half-push condition of the shutter button; then, the operator pushes the shutter button again to release the shutter.
A similar method can be used in the auto exposure adjusting operation, particularly in the spot photo-merry of a most important portion of the main object when the brightness of the object is strong, which method is called as "AE lock" and the like. Generally, the camera has the distribution of photometric sensitivity emphasized in the center of the view field; particularly in the spot photometry mode, there is photometric sensitivity only in the central portion of the field. Accordingly, after the brightness of the most important portion of the object is measured while positioning the most important portion in the center of the field, the measured value is stored or memorized in the half-push condition of the shutter button, and then, the operator shifts the main object in a desired position in the field to obtain a desired framing.
Such methods have some fundamental drawbacks as mentioned below, so that the automatic functions as mentioned above cannot be obtained adequately.
(a) In order to shift the main object in the picture to obtain the desired framing while maintaining the half-push condition of the shutter button, it is necessary for the operator to train his finger for maintaining the half-push condition of the shutter button correctly. However, since the most persons do not take a photograph frequently, they cannot easily manipulate such a camera that needs such a skilled technique.
(b) When the object to be photographed is moving toward or away from the camera, it is impossible to perform the above-mentioned automatic functions, because, even if the object is focused by the auto focus adjusting mechanism, the focused point is changed during the re-framing operation in the half-push condition of the shutter button. Further, when the object is moving laterally with respect to the camera in keeping a constant distance from the camera, great skill is requested for the operator to perform the above-mentioned stepping operations (from the focusing and/or exposure to the re-framing) correctly.
(c) When the object is an animal or a person who changes his facial expression and/or pose, since the opportunity to close the shutter exists only for a moment, the operator cannot obtain a desired picture through the above-mentioned stepping operations.
(d) When the camera is mounted on a tripod, it will be very difficult to adjust a camera angle while maintaining the half-push condition of the shutter button.
For these reasons, a new attempt in which the framing is not limited by the central distance measuring field and/or spot photometric function has been tried. More particularly, with respect to the auto focus adjustment, there has been proposed a camera including a multi point focus detection device having a plurality of auto focus detecting points presented in a wide area of the view field, and a camera which can selectively designate a portion of a wide focus detection field and the auto focus adjusting operation is performed on the basis of an object information obtained from the portion. These cameras are both already known. For example, in the former camera, the multi point focus detection device may be comprised of a plurality of conventional focus detecting elements arranged in the camera, as shown in FIG. 32. In the latter camera, the designation of the portion of the focus detection field (distance measuring field) can easily be performed through software by the use of a microprocessor usually incorporated in the automatic focusing camera.
Explaining FIG. 32 briefly, a picture frame 441 positioned in an expected focusing plane has five distance measuring fields 442a, 442b, 442c, 442d and 442e, and a conventional focus detection system is arranged in association with each distance measuring field. For example, in FIG. 32, a bundle of light beams of a focused image passed through a rectangular view field mask opening of the leftmost distance measuring field 442a is deflected by a leftmost lens portion of a integrally formed composite field lens 443 to be sent to a pair of secondary focusing lenses 444a.sub.1 and 444a.sub.2. A stop (not shown) is arranged in front of each pair of the secondary focusing lenses. The bundle of light beams passed through the secondary focusing lens 444a.sub.1 is focused as a light image of the field 442a on a photoelectric converter element (referred to as merely "photoelectric element" hereinafter) 445a.sub.1. On the other hand, the bundle of light beams passed through the secondary focusing lens 444a.sub.2 is focused as the light image of the field 442a on a photoelectric converter element 445a.sub.2. Since the above-mentioned stop (not shown) arranged near the secondary focusing lenses is focused substantially on a projecting pupil of a taking lens by means of the field lens, a so-called pupil division focus detection device is constituted by the aforementioned optical system. As shown, five focus detection devices so constituted are arranged in an array and are formed integrally with each other by structural members which can be assembled integrally.
With a hardware construction of such auto focus detection system, fundamentally, the distance measuring point can be determined by the following two methods
(1) The operator who takes a photograph designates a distance measuring position to be focused and inputs the designation information to the camera. The switch and dial can be used as the designation information inputting means.
(2) The camera analyzes the object information regarding each of the distance measurable points, or performs the distance measuring operation to automatically determine the distance measuring point on the basis of a predetermined reference. For example, the camera can automatically focus to the nearest object among from all objects positioned in the view field.
Both of the above two methods have some problems, and thus, have not yet been accomplished as a completely viable technique. More particularly, the above method (1), i.e., the method wherein the operator designates the distance measuring position for the camera has reliability; but, since it takes a long time to perform the inputting operation, the simplicity and speed inherent to the auto focus adjustment is lost. When the operator takes a photograph with the handy camera in a usual manner, a taking time will be shorter when the above-mentioned focus lock technique is used, than when the operator inputs the position designation information to the camera and then performs the focus adjusting operation. Accordingly, this method (1) has no merits, except when it is used in a photographing operation with the camera mounted on the tripod or is used in photographing the moving object where the position designation is required.
On the other hand, in the above method (2), i.e., the method wherein the camera itself performs the auto focusing operation automatically, it is frequently difficult to obtain the desired picture framing. When the camera automatically focuse on the nearest object at all times, all of the various photographing modes of the camera cannot be covered completely.
In conclusion, the above method (1) is reliable but is troublesome in operation, and the above method (2) is too uniform or standardized.
The consideration that the camera senses the visual axis of the operator to determine the distance measuring point is taught in the Japanese Patent Laid-Open No. 61-61135. However, this document does not disclose or teach the concrete method for detecting the visual axis. Incidentally, as a method for optically detecting the visual axis, a detection method using first and fourth Purkinge images reported in the literature "Accurate two-dimensional eye tracer using first and fourth Purkinge images" (Journal of the Optical Society of America, vol. 63, No. 8, page 921 (1973) and a detecting method using a first Purkinge image and a center of a pupil disclosed in the Japanese Patent Laid-Open No. 61-172552 are known.
When it is assumed that each of the curved surfaces of the cornea and of the lens of an eye is a spherical surface, the visual axis of an eyeball can be determined as a connecting line extending between the centers of the cornea and of the lens of eye. However, when a person is actually looking at an object, he gazes a certain point on an extension of a connecting line (visual axis) extending between the yellow spot on the cornea and the nodal point in front eyepart. Accordingly, there is a slight difference between the visual axis of the eyeball and the actual visual axis. As a result, if the direction of the visual axis is measured and accurate control is performed on the basis of the measured data, there will be fear of erroneous determination.
Incidentally, the method that the direction of the visual axis is detected photoelectrically to control the operation of the apparatus can be applied to the focus adjustment and/or direction adjustment in various inspection apparatuses, other than the camera having the auto focus adjusting mechanism.
Further, a recently developed camera includes manual input means for controlling various functions other than the auto focus adjusting function and auto exposure adjusting function, and many switches and displays for these functions are provided on the camera housing. However, an operator who does not use the camera frequently will forget the manipulation method for manipulating such switches, and thus, cannot utilize all of such functions effectively.